EP1814679B1 - Method for production of a seamless hot-finished steel tube - Google Patents

Abstract

In a method of making a seamless hot-finished steel pipe a billet heated to a shaping temperature is pierced by a first shaping to a thick-walled hollow ingot which subsequently undergoes a radial forging process using an internal tool inserted in the hollow ingot and at least two forging jaws of a forging machine. The forging jaws act on the outer surface area of the hollow ingot, wherein the hollow ingot is turned and axially advanced in a clocked manner in the idle stroke phase of the forging jaws.

Description

The invention relates to a method for producing a seamlessly hot-finished steel tube according to the preamble of claim 1.

After the invention of the brothers Mannesmann from a heated block to produce a thick-walled hollow block pipe, there have been various proposals to stretch this hollow block pipe in the same heat in another hot work stage. Keywords are the Kontiwalzverfahren, the Stoßbankverfahren, the plug rolling process and the Pilgerschrittverfahren ( Stahlrohr Manual, 10th edition, Vulkan-Verlag Essen 1986, III. Herstellverfahr s).

All these methods have their advantages for different dimensions and materials, although there are also overlaps. For the medium size range from 5 "to 18", the continuous and plug rolling process is used, for the size range up to 26 "the pilgrim stepping method is used.With thicker walls in the range of> 30 mm, the continuous and stopper rolling process are less suitable, while the pilgrimage process is has no problems with the wall thickness, but is slower in the production cycle.A disadvantage of all these methods are more or less long changeover times with dimensional change.

Characteristic of the production of seamless tubes from a heated block are the three steps of punching - stretching - reducing rolls ( H. Biller, The Seamless Tube Rolling - Problems of Process Selection, Stahl and Eisen 106 (1986) No. 9, pages 431-437 ).

Another method of seamless steel tubes is from the EP 0 610 509 A known for the production.

For some time, attempts have been made to save a step in order to reduce the manufacturing and installation costs. These efforts have been unsuccessful so far.

In the DE 1 906 961 A1 discloses a method for producing seamless tubes from continuously cast hollow bodies. In this known method, the cast strand is divided and the respective section is pre-stretched with the aid of an inner tool and hot forging. Thereafter, the prestretched portion is rolled on a continuous rolling mill to a pre-pipe (Luppe) and subsequently producing a finished tube by subsequent stretch reduction. This proposed method is intended to be applied to the mass production of small diameter tubes from continuously cast hollow bodies. The proposal is to help overcome the problem of heavy use of the skew rolls in pre-stretching.

The object of the invention is to provide a production method for seamless hot-finished steel tubes for the dimensional range of 5 "to 30" outer diameter and wall thicknesses ³ 0.1 x outer diameter for the range 5 "to <16" outer diameter or ≥ 40 mm wall thickness for the Range 16 "to 30" outer diameter is superior to the known method even for small batches in terms of deployment and productivity.

This object is achieved on the basis of the preamble in conjunction with the characterizing part of claim 1. Advantageous developments are the subject of dependent claims.

According to the teachings of the invention, the hitherto known second and third forming step characterized by rolling (drafting rollers and reduction rollers) is replaced by a forming step in the form of a radial forging process using an inserted into the hollow block inner tool and at least two acting on the lateral surface of the hollow block forging jaws of a forging machine, wherein the hollow block clocked in the phase of the idle stroke of the forging jaws is rotated and axially displaced. Depending on the type of control, the rotation and the axial feed of the hollow block can take place simultaneously or with a time offset.

The proposed method has the advantage that even thick-walled tubes can be produced optimally and the changeover times are low. Similar to the pilgrimage, the stretching process by forging still achieves a high elongation even with very thick-walled pipes. Thus, even with thick-walled pipes large pipe lengths can be displayed.
Another advantage is the fact that in most cases can be dispensed with the otherwise necessary downstream sizing mill, since after the drawing process by forging so produced ready-to-use pipe has finished tube quality.

The proposed forging process is then particularly effective and qualitatively favorable, if instead of two, a total of four forging jaws are used, which act synchronously in a plane on the lateral surface of the hollow block. For better distribution, in particular the thermal load, it may be advantageous to move the inner tool during forging in the same direction or opposite to the axial feed.

For large degrees of stretch (> 4) and small wall thickness (<30 mm), it may be necessary, before forging in the hollow block a release and lubricant z. B. on Phosphaterm- or graphite-based. This avoids that it comes to a caking of the forged hollow block on the inner tool.

The first forming step may optionally be a hole punching or a punching by means of oblique rolls. After the hole pressing the soil is separated or pierced. The separation can be done by flame cutting or hot sawing. The hollow block produced by punching or by punching by means of oblique rolls can be forged directly or pre-stretched by a subsequent oblique rolling before it receives its finished pipe dimension by forging.

In this procedure, the separation or piercing of the soil can be omitted after the hole pressing. For skew rolling, a two-roll or three-roll machine is used. Depending on the preliminary process, descaling of the outer and / or inner surface is advantageous.

The forged ready-made pipe is either immediately ready for delivery after the usual finishing steps such as cutting to length, visual inspection, marking etc. or is first subjected to a heat treatment and / or a non-destructive test. The heat treatment may be normalizing or tempering. Depending on the straightness requirement, straightening is required. Likewise, with appropriate delivery requirements, over-sanding or other suitable chip-removing machining of the outer surface may be necessary to eliminate the small bumps caused by the forging process.
The starting block to be used is either a section of a continuous casting rod, preferably a round-strand casting rod or ingot. Depending on the hole process used, a pre-deformation of the material can be difficult to form Continuous casting by rolling or forging may be required. The heating of the output block is carried out in a known manner in a rotary hearth or in a walking beam furnace. At high weights, other heating furnaces, such. B. Tieföfen conceivable.

Based on schematic representations, the inventive method will be explained in more detail below.

Figur 1

das erfindungsgemäße Verfahren mit einem Lochaggregat (Schrägwalze),

Figur 2

das erfindungsgemäße Verfahren mit einem Lochaggregat (Schrägwalze) und einem nachgeschaltetem Vorstreckaggregat (Elongator).

Figur 3

im Längsschnitt einen im Eingriff sich befindenden Hohlblock

Figur 4

ein Schnitt in Richtung A - A in Figur 3

Show it

FIG. 1

the method according to the invention with a perforating unit (inclined roller),

FIG. 2

the inventive method with a hole assembly (oblique roller) and a downstream pre-stretching unit (Elongator).

FIG. 3

in longitudinal section an engaged hollow block

FIG. 4

a section in the direction A - A in FIG. 3

FIG. 1 shows a schematic representation of the inventive method with only one hole assembly as the first forming step. By way of example, a block 1 divided off from a steel continuous casting rod is placed in a rotary hearth furnace 2 and heated to a deformation temperature, eg. B. 1250 ° C, heated. After heating and leaving the rotary hearth furnace 2, the heated block is fed via a roller table 3 a punching unit.

In this embodiment, the perforating unit is designed as a cross rolling mill 4 with two oblique rollers 5, 5 '. This includes an inner tool consisting of a piercer 6 and a support rod 7. Since the punching by means of oblique rollers is well known, it is unnecessary to take a closer look at it.
By punching a block 8 has been produced from the block 1, which passes through a transverse transport 9 to the forging machine 10. The following stretching process by radial forging forms according to the invention the summary of the otherwise customary second and third forming step instead of the usual rolling, be it as a continuous, stopper or pilgrim step method with downstream reduction rolls.

After retraction of an inner tool 11, preferably in the form of a cylindrical dome, the hollow block 8 is transported by a arranged on the inlet side manipulator 13 longitudinally through the forging stand 14 and simultaneously rotated. This rotation and the axial feed of the hollow block 8 is clocked in the phase of the idle stroke of the forging jaws either simultaneously or offset in time.

Later on, a second manipulator 12 takes over the finished tube 16 on the outlet side in order to complete the forging process. The forging unit is shown here only schematically and has here, not shown, the hollow block 8 encompassing forging jaws, which act on the lateral surface in order to stretch by reducing both the outer diameter and the wall thickness of the hollow block 8.

After the drawing process by forging, the ready-to-use tube 16 is transported according to the arrow 15 into the finishing line in order to make it ready for shipment there. The finishing usually comprises a cutting to length, a visual inspection, a marking and, depending on requirements, a previously performed heat treatment and / or a non-destructive testing. For reasons of space, the hot-finished tube 16 is shown shorter than would correspond to the extension.

By way of example, according to the in FIG. 1 illustrated workflow of a block 1 with the dimension 406 mm round and a length of 2.8 m after punching a hollow block 8 of the dimension 390 aüßerer diameter x 123 mm wall thickness produced with a length of 3.5 m. After forging, the hot-made tube 16 has an outer diameter of 203 mm with a wall thickness of 50 mm and a length of 15 meters.

FIG. 2 shows a variant of the method according to FIG. 1 , wherein like reference numerals have been selected for like parts. The first forming step is identical to that until the production of a hollow block 8 FIG. 1 explained forming step.
Before the stretching process by forging, the second forming step, however, a Vorstreckaggregat, a so-called Elongator 17, is arranged. Also, the Elongator is formed in this embodiment as a cross rolling mill with two inclined rollers 18, 18 'and an inner tool, consisting of a plug 19 which is connected to a support rod 20.

The hollow block 8 leaving the perforating unit is fed via a transverse transport 9 to the input side of the elongator 17. By the oblique rolling of the hollow block 8 is pre-stretched and reduced in the wall thickness hollow block 8 'produced. The diameter of the hollow block 8 'may be equal to, smaller or larger after Vorstrecken.

Thereafter, the hollow block 8 'via a transverse transport 9' already in FIG. 1 explained forging machine 10 supplied. Since the following steps are identical, a repetition is unnecessary.

By way of example, according to the in FIG. 2 illustrated workflow of a block 1 with the dimension 500 mm round and a length of 4 m after punching a hollow block 8 of the dimension 500 mm aüßerer diameter x 180 mm wall thickness produced with a length of 4.3 m.

After passing through the Elongators is a hollow block 8 'with the dimensions 480 mm outer diameter x 120 mm wall thickness and 5.8 m length before.

After the forging process, the ready-to-use pipe 16 has an outer diameter of 339.7 mm, a wall thickness of 75 mm and a length of 12.6 m.

FIG. 3 shows in a longitudinal section an engaged to be forged hollow block 8, which runs from the left into the forging machine and right as a ready-to-use pipe 16 leaves the forging machine. In the forging area, four forged jaws 21, 21 'act on the outside in this exemplary embodiment. 21 ", 21 '" and on the inside a cylindrical mandrel 22 together. The mandrel 22 is held in place by a support rod 23, but may alternatively be moved axially forward or backward during the forging process.

The rotary arrow 24 and the axial arrow 25 are intended to illustrate that during the idle stroke of the forging jaws 21 - 21 "'the hollow block 8 is rotated and pushed further axially.

Each forging jaw 21-21 '"has in longitudinal section a predominantly conically shaped inlet section 26 and an adjoining smoothing section 27. The inlet section 26 can also be slightly convexly curved.

Seen in cross section ( FIG. 4 ) , all the forging jaws 21 - 21 "'have a concave curvature, as a rule, the curvature is a circular arc whose radius is greater than the current radius of the part to be forged.

The in the Figures 3 and 4 drawn movement arrows 28 are intended to illustrate the radial stroke of the respective forging jaw 21 - 21 "'.

LIST OF REFERENCE NUMBERS

No. description 1 block 2 Rotary hearth furnace 3,3 ' roller table 4 Piercing mill 5.5 ' skew roll 6 piercer 7 Handrail 8th hollow block 9.9 ' cross transport 10 forging machine 11 internal tool 12 Manipulator, outlet side 13 Manipulator, inlet side 14 forging stand 15 transportation arrow 16 ready to use pipe 17 elongator 18, 18 ' skew roll 19 Plug 20 Handrail 21, 21 ', 21 ", 21"' forging jaw 22 mandrel 23 Handrail 24 rotation arrow 25 Axialpfeil 26 inlet section 27 smoothing part 28 movement arrow

Claims (20)

1. A method of manufacturing a seamless hot-finished steel tube, wherein, starting from a block heated to shaping temperature, a thick-walled hollow block is produced in a first shaping step by piercing and is then drawn at the same temperature in a second shaping step by rolling, during which the diameter and the wall thickness change, to form a rough tube (bloom), and a finished tube is produced therefrom in a third shaping step by reduction rolling, characterised in that the second and third shaping steps defined by rolling are replaced by a shaping step in the form of a radial forging process using an internal tool inserted into the hollow block and at least two forging jaws of a forging machine that act on the outer surface of the hollow block, wherein the hollow block is rotated and axially displaced in a timed manner in the idle stroke phase of the forging jaws.
2. A method according to claim 1, characterised in that the rotation and the axial feed of the hollow block take place simultaneously or in a temporally staggered manner.
3. A method according to claims 1 and 2, characterised in that four forging jaws are used which act synchronously on the outer surface of the hollow block in one plane.
4. A method according to claims 1 to 3, characterised in that the internal tool is stationary during forging.
5. A method according to claims 1 to 3, characterised in that the internal tool is moved in the same direction as the axial feed during forging.
6. A method according to claims 1 to 3, characterised in that the internal tool is moved counter to the axial feed during forging.
7. A method according to any one of claims 1 to 6, characterised in that a releasing and lubricating agent is applied to the inside of the hollow block before commencement of the radial forging process.
8. A method according to any one of claims 1 to 7, characterised in that the first shaping step is punching.
9. A method according to claim 8, characterised in that the base is broken through after punching.
10. A method according to claim 8, characterised in that the base is removed after punching.
11. A method according to claims 8 to 10, characterised in that the hollow block is internally and externally descaled after punching and removal of the base.
12. A method according to claim 8, characterised in that rough drawing takes place by means of diagonal rolling after punching.
13. A method according to claim 12, characterised in that the hollow block is internally descaled after diagonal rolling.
14. A method according to any one of claims 1 to 7, characterised in that the first shaping step is piercing by means of diagonal rolling.
15. A method according to claim 14, characterised in that rough drawing takes place by means of diagonal rolling after piercing.
16. A method according to claims 14 and 15, characterised in that the hollow block produced is internally descaled.
17. A method according to any one of claims 1 to 16, characterised in that the finished tube undergoes heat treatment.
18. A method according to any one of claims 1 to 17, characterised in that the finished tube is straightened.
19. A method according to any one of claims 1 to 18, characterised in that the outer surface of the finished tube is machined.
20. A method according to claim 19, characterised in that the machining is a grinding process.

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